>> And here is the explain analyze: http://explain.depesz.com/s/4xm >> It clearly shows a bitmap index scan operation is immediately followed >> by a recheck operation AND that the recheck operation actually does >> something, because it reduces the number of records from 61 to 58 >> (!!!). > > > That could be ordinary visibility checking, not qual rechecking.
Visibility as in transaction-wise? It's not, this was the only client connected to the dev server, and the only transaction(s) happening.
I guess Jeff meant the visibility of tuples, in this case there may have 3 rows that are referenced by the index but are not visible to your current transaction (they may be visible by other transaction or simple hasn't been marked by VACUUM).
If you have no concurrent transactions, you can run VACUUM on your table, run the query again and see if the row counts matches.
Best regards, -- Matheus de Oliveira Analista de Banco de Dados Dextra Sistemas - MPS.Br nível F! www.dextra.com.br/postgres